For those having troubles on the 800PP races, might I suggest the NSX GT500 (formally known as the Epson NSX in GT-S). That thing doesn't get the credit it deserves, as it's a bit slower than the other Gr2 cars, but it is better than the Gr3 cars, IMO.
On RH tires it comes in just under 800PP. It's great on tires, great on fuel, and has great aero for going through the turns. It lacks a bit on the straights (you can add a turbo to mitigate this but the PP goes well over 800), so LeMans might now be the best, but I won the Daytona 800PP with it pretty easily. Haven't tried Suzuka yet but when I do I'm going to use the NSX. Car is underrated, IMO.